Mussel Glossary

This
glossary will introduce the special names of the specific parts of a
mussel, and the scientific terms for the functions, processes, and activities
associated with mussel anatomy and life cycle. There are several labeled
drawings to assist users with mussel anatomy.

a pair of
muscles that close the two valves of a mussel shell. Each muscle
extends from the left valve to the right valve, one in the anterior
part of the shell and the other in the posterior part.

anterior
end (noun)

front end
of a mussel where its foot protrudes and its beak is located.

beak
(noun)

the raised
portion of the dorsal margin of a shell, also called the umbo.
The beak is the oldest portion of a mussel shell, formed when
the animal was very young.

beak cavity
(noun)

the depression
or cavity on the inside of each valve beneath the beak.

beak sculpture
(noun)

natural
surface markings on the beak, consisting of raised loops, ridges,
or bumps.

bivalve
(noun)

a type of
mollusk with a shell consisting of two valves (Class Bivalvia).

byssus
threads (noun)

a bundle
of tough threads secreted by a gland in the foot of the zebra
mussel (Dreissena polymorpha) and some other bivalves,
used to anchor it to a hard object. The glochidial larvae of some
pond mussels (e.g., Anodonta suborbiculata) also possess
long byssus threads, which form underwater "nets" or "webs" that
probably aid the attachment of larvae to host fish.

chevron
(noun)

a V-shaped
marking.

compressed
(adjective)

flattened
or pressed together from side to side.

concentric
(adjective)

having a
common center, such as a series of ridges or loops radiating outward
from the beak of a mussel shell.

distal
(adjective)

situated
away from a point of origin or attachment.

dorsal
(adjective)

pertaining
to the top or back of an animal; in mussels, the hinge area.

elliptical
(adjective)

having the
form of an ellipse (an elongated circle).

elongate
(adjective)

having a
long or extended shape.

exotic
species (noun)

a species
of foreign origin, not native to an area where it occurs. Asian
clams (Corbicula fluminea) and zebra mussels (Dreissena
polymorpha) are exotic species in North America that were
introduced by humans in the 20th century.

extirpated
(adjective)

a species
that has become extinct within a portion of its range.

foot
(noun)

a muscular
organ that a mussel uses to anchor itself in the substrate or
move from one place to another.

gills
(noun)

platelike
respiratory organs in freshwater mussels that also help gather
food particles ("filter-feeding") and provide a place for female
mussels to store their glochidial larvae (marsupium).

glochidia
(noun)

bivalved
larvae of freshwater mussels, which are generally parasitic on
a fish host.

growth
lines (noun)

concentric
lines on the outside of a shell that indicate periods of arrested
growth. Extended periods of growth arrest occur during winter,
forming darker or thicker growth lines.

hinge
(noun)

the dorsal
part of a mussel shell where the left and right valves attach.

hinge
ligament (noun)

an elastic
structure that unites the two valves of a mussel along the top
of the shell.

hinge
teeth (noun)

interlocking
triangular or ridge-like structures located along the hinge of
some mussels, which serve to keep the valves in alignment (pseudocardinal
and lateral teeth).

inflated
(adjective)

swollen
or expanded from side to side.

interdentum
(noun)

the portion
of the hinge between the pseudocardinal and lateral teeth.

iridescent
(adjective)

displaying
an array of colors like those of a rainbow.

labial
palp (noun)

an appendage
of soft tissue that channels food particles to the mouth.

larva
(noun)

immature
form of an animal that undergoes complete metamorphosis.

lateral
teeth (noun)

elongated,
interlocking ridge-like structures (hinge teeth) located along
the hinge of some valves.

left valve
(noun)

the left
half of a mussel shell, which can be identified by orienting the
shell with the hinge facing up and the anterior end forward (away
from the observer).

mantle
(noun)

soft tissue
enclosing the body of a mussel, the principal function of which
is to secrete the shell. In some species of the Subfamily Lampsilinae,
the posterior portion of the female mantle serves to attract host
fish by mimicking the shape and movement of fish or crayfish.

a pit or
depression marking the attachment of a muscle to the inside of
the shell. For example, the anterior adductor muscle scar is the
point of attachment for the anterior adductor muscle.

nacre
(noun)

the lustrous
interior layer of mussel shell, which is composed of shingle-shaped
crystals of calcium carbonate (CaCO3). Usually white, pink, salmon,
or purple, and often iridescent. Also called the "mother-of-pearl"
layer.

oblong
(adjective)

having an
elongated shape, which may be rectangular or elliptical.

ovate
(adjective)

having the
shape or outline of an egg; egg-shaped.

pallial
line (noun)

a linear
groove on the inside of a shell marking the line of attachment
of the mantle to the shell.

periostracum
(noun)

exterior
organic layer of mussel shell, which may be yellow, green, brown,
or black and is sometimes marked by green rays. The periostracum
protects the calcareous layers of shell (nacre and prismatic)
from dissolution by acids in water.

plications
(noun)

parallel
ridges or folds on the outer surface of a shell.

posterior
end (noun)

rear end
of a mussel where its inhalent and exhalent siphons are located.

posterior
ridge (noun)

a ridge
on the exterior of a mussel shell that extends from the beak to
the posterior margin.

posterior
slope (noun)

the area
on the exterior of a valve extending from the posterior ridge
to the dorsal margin.

prismatic
layer (noun)

the middle
layer of mussel shell, which is composed of column-shaped crystals
of calcium carbonate (CaCO3).

pseudocardinal
teeth (noun)

triangular,
often serrated structures (hinge teeth) located near the anterior-dorsal
margin of some valves.

pustule
(noun)

a small
bump or raised knob on the outer surface of a valve, also called
a tubercle.

quadrate
(adjective)

square,
or nearly square, in outline.

ray
(noun)

a linear
color marking, usually green, which appears on the outer surface
(periostracum) of some mussel species.

ridge
(noun)

an elongate
elevation on the outer surface of a valve. Multiple parallel ridges
form plications or undulations.

right
valve (noun)

the right
half of a mussel shell, which can be identified by orienting the
shell with the hinge facing up and the anterior end forward (away
from the observer).

sculpture
(noun)

raised natural
surface markings on the outside of the shell, consisting of knobs,
pustules, ridges, or spines.

serrated
(adjective)

notched
or grooved.

sexual
dimorphism (noun)

a condition
in which males and females of a species differ from one another
in shape. Evident in some female mussels by an enlargement or
extension of the posterior-ventral part of the shell.

shell
margin (noun)

the outer
edge or circumference of a valve when laid flat.

siltation
(noun)

the deposition
of silt (fine mud) on the bottom of a river or lake, which, in
great amounts, may threaten mussel survival.

siphon
(noun)

Opening
on the posterior end of a mussel, formed by the mantle tissue,
which allow for the circulation of water inside the animal. Water
enters through the inhalent siphon and is expelled through the
exhalent siphon.

solid
(adjective)

thick or
heavy shell.

spawn
(verb)

in reproduction,
the release of sperm or eggs in water.

striated
(adjective)

marked with
numerous parallel furrows or grooves.

sulcus
(noun)

a shallow,
elongate furrow or depression on the outer surface of a shell
that generally extends from the beak to the posterior or ventral
margin.

truncate
(adjective)

having an
end that appears to be shortened or squared off.

tubercle
(noun)

a raised
bump or projection on the outside of a shell, also called a pustule.

umbo
(noun)

the raised
portion of the dorsal margin of a shell, also called the beak.